A so-called night-vision system mounted in a vehicle has been put into the practice recently (refer to patent literature 1). This type of night-vision system includes a light projector that emits near infrared lights to a specific space defined in the vicinity of the subject vehicle in which the system is mounted, an image taking device that receives lights including the near infrared lights from the specific space and produces an image, and a display device that displays the image produced by the image taking device.
Further, the night-vision system may detect a target object, such as a pedestrian, based on an image produced by the image taking device, and report the presence of the detected object.
It is required for the night-vision system that to upgrade visibility of an image displayed on the display device and to provide an image produced by the image taking device included in the night-vision system in color display.
For meeting the requirements, the image taking device employed in the night-vision system may include multiple light receiving elements that are arranged in the form of a mosaic (matrix), visible light passing filters that transmit visible lights, and near infrared passing filters that transmit near infrared lights.
In recent years, windshields capable of cutting light having wavelengths which fall within an infrared wavelength range have been employed in vehicles for suppressing a temperature rise in a compartment of the vehicle. An adoption of this kind of windshield may decrease an intensity of the near infrared lights, which are reflected from a target object and received by the image taking device. Accordingly, an image produced based on the light received by the image taking device may fail to display the detected object in highlighted manner. In order to display the detected object in highlighted manner, the intensity of near infrared lights may be multiplied by a gain to amplify the intensity of near infrared lights received by each of light receiving elements via each of near infrared passing filters. When the intensity of near infrared lights is amplified, numerous tiny grains or specks that are brighter than the background may appear on the image due to amplification of a noise component of the intensity of near infrared lights received by each of the light receiving elements via each of the near infrared passing filters. When the intensity of near infrared lights is amplified, a flare originally included in the image may be further intensified. The appearance of numerous brighter grains or specks on the image or the intensifying of the flare may decrease a brightness contrast of an image. A decrease in brightness contrast of an image degrades not only a visibility of an image displayed on the display device but also makes a detection of a target object included in the image difficulty for an image processing apparatus included in the night-vision system.